We don't all suck. Some definitely do. Just like anything else in life, you should research your doctor before you accept him/her.
In an emergency, you stuck with what you got, unfortunately.
Very few doctors are lazy-- there are a lot of easier ways to make money, trust me- but some are burned out and others have functionally thrown in the towel battling a system that is fundamentally flawed and crumbling, particularly primary care.
I'm sorry the system and the doc failed your Mom. You should be mad and its unforgivable.
The lawsuit is not a slam dunk like you might think. You need to establish violation of the standard of care, harm and causation. The first two are definite here but proving causation is not easy. If she needs a pancreas/kidney transplant then the CMPA may argue that antibiotics would have very little impact on the progression of infection in an immunocompromised, neuropathic, ischemic digit. They're probably right, too-- but that doesn't mean antibiotics shouldn't have been tried early on. You might run it by a lawyer who may agree to take it on without a retainer. More likely, he/she will tell you not to bother as the payout v.s. the cost will not be favourable.
There is something you can do something on your mother's behalf that might make a large impact, though. You can write a letter to the provincial college of physicians and surgeons (Google it and click on the complaints link). Write them a letter that is nice and calm with all the facts. No emotional stuff, just the facts. Tell them you expect the doc to be investigated and you want to be kept abreast of the investigation. They have to do it or give you a reason why not. Be patient as the process can take years sometimes. It WILL make his life miserable and he will think twice before treating another patient like your Mom in that manner again. If this is a pattern he may lose his licence temporarily or even permanently.
In the old days, even 10 years ago, there was a lot of covering for each other. Definitely NOT anymore. Lawyers have no problems finding expert witnesses to testify against colleagues (I do it) and the College is much more aggressive about investigating and disciplining the members on behalf of the public lately. M&M rounds (morbidity and mortality rounds) where we discuss bad results and flagged complaints etc have become known as "blood letting rounds".
Hope your Mom is feeling better and gets her organs soon.
l

